1. Field of the Invention
The present invention is directed to a dexterous hand, more particularly a modular dexterous hand in which the functions of grasping and fine manipulation are carried out by separate stages of the hand.
2. Background of the Related Art
Numerous devices have been proposed as grasping hands for use with robot arms. The simplest consist of simple parallel jaw grippers. However, the resulting two-point grasping contact has been found to be insufficient to prevent rotation of the grasped object, except in special cases.
More complex systems include anthropomorphic designs which are suitable for master/slave control by a human operator. Jacobsen, Wood, Knutti and Biggers; "The Utah/MIT Dexterous Hand: Work In Progress" (The International Journal of Robotic Research, vol. 3, No. 4, 1984). However, anthropomorphic designs are relatively complex. Moreover, since the fingers are multi-jointed, the fingertips pivot about axes perpendicular to the length of the fingers, so that the fingertips do not always move within a single plane. This makes it complex to grasp small objects lying on flat surfaces such as tabletops.
Another problem with anthropomorphic designs is that both grasping and fine manipulation are provided by the same structure, although this feature is not limited to anthropomorphic designs. This coupling implies that fine manipulation of the grasped object will involve rolling the object between the fingertips, and this can result in a loss of positional certainty of the object if a precise knowledge of the shape of the object near the contact points is not well known.
U.S. Pat. No. 4,653,793 (Guinot et al) discloses a multiple point contact gripper in which three grasping fingers are movable linearly toward and away from one another to form a deformable grasping triangle at their tips. Two of the finger tips are formed by rotatable balls while the other is formed by a ball fixed to the finger tip. However, since the fingertips must move linearly, it is difficult to grasp small objects, and obstructions in the path of movement of the fingertips can make grasping difficult. In the embodiment of FIG. 8 of Guinot et al, the fingertips pivot about axes perpendicular to the length of the fingers, and so suffer from the same shortcomings as do those of anthropomorphic hands, i.e., the fingertips do not remain in a plane as they move, which makes it difficult to pick up objects, especially small objects, from tabletops.